Several techniques are utilized to print images on manufactured goods, such as drink and cosmetics containers. These containers are made of various materials, such as plastics, metals, and coated paper, and the traditional method for placing images on these containers, sometimes called “imaging” a container, is to print a label on a plastic or paper substrate and then affix the pre-printed label onto the container with adhesive. However, during the last 20 years many manufactures have transitioned from label printing to direct printing onto the container surface, sometime referred to as “direct-to-shape” (DTS) printing. However, while a label is a flexible medium and may be printed using traditional flexible sheet printing using methods going back over 100 years, direct printing on containers poses many challenges. One challenge is that while paper readily absorbs and retains inks and is a well understood medium for imaging, the containers themselves are made of materials that are difficult to image. Inks of special chemical blends and additives must be used, sometimes in the presence of active drying or hardening processes such as catalyst exposure or fast-curing using ultra-violet (UV) radiation. Further, container shapes are fixed, and an imaging process must take into account the irregular and varied shapes of the containers that are to be imaged. Such challenging print surfaces comprise a good-many products, such as drink cans and bottles, home care products, cups, coffee tumblers, personal care items, automotive parts, sports equipment, medical products, and electronics containers to name just a few. Hence, choosing the proper type of DTS printing equipment largely depends on the shape, size, number of colors, and type of substrate to be imaged, as well as the method that is preferred in which to transfer the image onto the substrate surface.
Various techniques have been developed to achieve DTS printing. One technique, “pad printing,” allows the transfer of a two-dimensional image onto a three-dimensional surface through the use of a silicone pad, an ink cup, and an etched plate. Pad printing is ideal for difficult substrates such as products found in the medical field and promotional printing, but due to the expense of the process pad printing typically uses only 1 or 2 colors during a print job.
Another technique, screen printing utilizes a mesh or screen to transfer the ink to the substrate surface. The process requires creating a screen that selectively permits ink to flow through the screen using a blocking stencil. While a photographic process may be used to create a screen, and hence allows relatively good resolution of imaging, the process requires substantial set-up time and is less flexible because any update or small alteration to the image to be laid down requires the creation of a new screen set. In addition, screen printing is typically restricted to only 1 or 2 colors because each color requires its own separate customized screen.
Inkjet DTS printing has over time risen to be a preferred method for DTS printing, especially for package printing. Inkjet printing utilizes a digital printhead to print full color customized designs in one or multiple imaging passes and may be applied directly to the substrate surface of the object or medium. Developed in the 1970s, inkjet printers were created to reproduce a digital image on a printing surface. The transfer occurs by propelling droplets of ink directly onto the substrate medium. The ink delivery mechanism is called the “printhead,” and is controlled by a digital image held by a connected computer system and which may be altered an infinite number of times. However, the design of printheads in an inkjet system varies greatly. Each head is uniquely designed for its application, and a variety of digital printers designs are available to be used to print on various substrates. Hence, various factors drive the types of inkjet printing system to be utilized for a printing project, such as the type of product substrate to be printed, the volume of products to be printed, and the required manufacturing speed for the imaging of any product traversing through the manufacturing line.
However, the benefits of inkjet printing in DTS applications have driven a recent preference to use inkjet systems in product manufacturing lines. For example, inkjet printing requires less set-up time and allows for faster print and cure times. Inkjet printing also is configurable to allow printing on multiple items at once, whereas other printing methods are often restricted to a single print instance for each object being printed. Moreover, print jobs do not require fixed setup time and costs, such as the generation of screens or the installation of plates.
On great advantage of inkjet printing is the ability to change graphic images quickly, sometimes almost in real-time, to adjust for printing results. Modern imaging software is template driven and allows for the importation of new or re-worked graphics instantly. Hence, the flexibility of image alteration on a job-by-job basis is a distinct advantage.
In addition, inkjet printers are robust enough to be used for short and long printing production projects, thereby meeting various manufacturing demands. For example, single machine may be used to prototype or provide a sample, low-volume job for a potential client, or that same machine may be used in the same facility to print thousands of articles in a day. Further, the same machine may use various types of inks to accommodate different object substrate materials.
Finally, conveyor and assembly line capability allow the inkjet printing process to become automated which can increase productivity and lower labor costs. So-called “inline” printers can do such printing at incredibly fast production rates. Typically, the inkjet printhead remains stationary while the substrate is moved past the printhead. This type of inkjet system is ideal for barcoding and dating product packaging. Single-pass multi-color inkjet printers are similar sometimes offering higher quality imaging with more color options at slightly slower print speeds.
One type of inkjet system is specialized to print on the surface of cylindrical containers and are called “digital cylindrical presses.” For example, The INX Group Ltd. (aka “Inx Digital” and “JetINX”) a division of Sakata INX offers a cylindrical printing solution under its CP100 and CP800 line of direct-to-shape (i.e. DTS) inkjet printing systems. These systems allow for the creation of an inkjet production line to print directly onto axially symmetrical objects. Other companies offer similar systems, such as Inkcups Now Corporation which offers the Helix line of DTS printers. These printers use a rotatable mandrel to hold an object and rotate the object next to an inkjet printhead as the printhead jets ink onto the surface of the cylindrical object. An image is captured for transfer onto an object and a printing “recipe” created, either by the printing machine itself or separately on personal computer and then imported into the printing machine. The “recipe” includes information necessary for the printing an image onto a media object and the recipe parameters are specific to each type of printer utilized.
The CP100 machine is a good example of an industry standard cylindrical DTS printing system. The system is a stand-alone machine that performs non-contact printing of images on generally cylindrical objects, particularly hollow cylindrical objects or hollow partially-cylindrical objects, for example, cans and bottles and including two-piece cans and bottles. Each cylindrical object is hand-loaded onto the machine and secured by vacuum on a mandrel to prevent slippage, which is part of a carriage assembly that functions to linearly positioning the object beneath at least one digitally controlled inkjet printhead. The object is rotated in front of the printhead while ink is deposited to the object to produce a desired printed design on the object. The ink is either partially or fully cured immediately after printing by exposing the ink to an energy-emitting means, such as a UV light emitter, positioned directly beneath the object. A carriage assembly is fixedly mounted to a linear slide actuator, which is in turn fixedly mounted to a mounting frame, whereby the carriage assembly is free to traverse along the linear slide actuator. The carriage linearly advances the object in a position adjacent to the inkjet printhead such that a first portion of the object may be printed if the object length is longer than the length of the printhead. The object is rotated while the computer-controlled printheads deposit ink from a supply of ink located above the object being printed upon. Simultaneously the UV light emitter either partially or completely cures the ink. The carriage then continues to advance the can further such that the entire length of the can is printed. As may be understood, the continuous advancement of the object by the printhead may not be necessary if the printhead is longer than the image desired to be printed on the object. The image itself comprises a digital image that is imported from a separate imaging application and loaded into application that creates a “recipe” of the image based on the physical specifications of the object to be printed upon. The profile is loaded through an operating system present on the machine and utilized to control motion of the object held by the carriage assembly along the linear slide. A print engine running on the machine controls the delivery of ink onto the object via the inkjet printhead as the object is moved past the printhead in a digitally controlled manner. The precise deposition of the ink via the inkjet heads onto the object, is dependent upon the object recipe which includes the specific amount and color of ink applied to the object as it traverses the printhead. The structure and operation of standard cylindrical DTS printing systems are fairly well understood in the printing industry and disclosed in representative U.S. Pat. Nos. 6,918,641B2 and 7,967,405B2.
However, the machines offered by Inx International only print onto a cylindrically flat exteriors and do not allow for the printing over curved exteriors of axially symmetric objects, such as exists on tapered drink tumblers or 3-dimensionally contoured bottle shapes.
The above-mentioned Helix line of cylindrical printers offered by Inkcups does allow for DTS printing of axially symmetrical, tapered drinkware, such as common stainless-steel drink tumblers. The Helix printer achieves this by tilting a mandrel holding the object to be printed and adjusting the angle of the object relative to a stationary printhead to approximate a straight line over a contoured surface of the object. The problem with the Helix approach is that such straight-line approximation does not ensure a constant density of ink to be applied to the object because the print head moves outside of an optimal jetting distance due to the fixed length of the print head. This non-optimal positioning of the object in relation to the printhead results in unacceptable color shifts in the printed image and various image issues due to increased ink drop drift and overspray. Since these types of cylindrical printers cannot provide constant articulation of the head or media throughout the print cycle to minimize the jetting distance, the Helix and similar printers are limited to printing on axis symmetrical shapes that are approximately cylindrical or conical where the gap between the printhead and printed surface can be maintained at a distance that does not exceed the capability of the printhead to provide acceptable dot placement and image quality. Hence, these types of printers are limited in the types media on which they may print because most contoured media objects will exceed the printhead capabilities of these printers (e.g. greater than 5 mm jetting distances), thereby not being able to produce a quality image.
Therefore, which is needed is a system that allows for inkjet printing along a 3-dimensionally contoured surface of an object during direct-to-shape or DTS imaging that provides superior color imaging over a contoured surface where approximating the shape as a cylinder or cone does not provide acceptable image quality due to the printhead being too far away from the continually varying printed surface.